Lease or buy or finance or what?

As with buying a car, it's good to consider not just the initial purchase price, but the total price of ownership. In this case, that means factoring in the price of service. You also need to decide if you can swing the full price of the phone up-front or if you'd prefer to finance it.

For example, if you buy the S9 or S9 Plus directly from Samsung, you'll get it unlocked and pay $720 or $840, respectively. Can't afford that much? Samsung has a no-interest financing program: $30 per month for 24 months for the S9 ($720 total) and $35 per month for the S9 Plus ($840 total).

From there you can take the phone to whatever carrier has the best bring-your-own-device deal on service, including a wide range of low-cost MVNOs: Boost Mobile, Consumer Cellular, Cricket, MetroPCS, Tello, Ting and so on.

For example, Cricket offers a no-contract plan that includes 5GB of high-speed data (unlimited after that) for $35 per month with auto-pay.

The Big Four carriers will also finance an S9 for you, with monthly rates that are mostly within a few dollars of one another. However, these deals usually require you to sign up for an unlimited service plan as well, and those range from $60-75 per month.

Let's go to the calculator

Math will tell us what we need to know. Let's focus just on the S9 for now. You can easily figure out the equivalent price for the S9 Plus using any of these equations.

As noted above, different carriers will be charging different rates for the phone. If you go with, say, Verizon, you'll pay $33.33 per month for 24 months -- plus $75 per month for service. Grand total after two years: about $2,600.

AT&T draws out the financing to 30 months, with a $26.34 monthly payment and minimum $60-per-month service plan. That adds up to about $2,590 after two and a half years.

Now let's say you pay Samsung $30 per month for your S9 and Cricket $35. (I realize the latter is nowhere near an apples-to-apples comparison to a Big Four carrier, but the reality is that many of us use less than than 5GB of high-speed data each month.) Grand total after two years: About $1,560.

Needless to say, the smart money is on buying from Samsung, then choosing whatever carrier best meets your needs. And because your Samsung model will be unlocked, you can easily hop from carrier to carrier as deals change. You're not stuck with the same one for two years while you pay off the phone.

Hang on, though -- there are some other variables to consider.

Trade-ins, credit and beyond

Before you turn your back on the Big Four, check out their trade-in options. T-Mobile and Verizon will credit you up to $350 when you trade in your current phone. (Check each carrier's promo page for eligibility, rates and details.) Best Buy is also offering trade-in credit, but only when you sign up for service with AT&T, Sprint or Verizon.

Thankfully, there's a similar Samsung option here as well: You can trade in an eligible phone as part of your outright-purchase or financing deal.

Of course, the amount of credit you'll get anywhere varies depending on the age and model of your trade-in -- and you can often do better by selling the phone yourself for cash.

Finally, there's something to consider beyond money: OS updates. Historically, Big Four carriers have pushed out Android updates faster than Samsung and MVNOs. If that's important to you, you may want to stick with a Big Four carrier.

What are your thoughts on the S9 and S9 Plus? Think you'll go with a carrier? Finance it with Samsung? Live with your perfectly good current phone for another year or two? Share your thoughts in the comments!